Complement system play a role in preventing inflammation and joint immobility. Osteoarthritis (OA), an inflammatory disease of the joints, is quite prevalent among the elderly and causes disability in nearly 10% of the population over 55 years. Current medications only manage the disease and do not cure or halt the disease. The prevalence of OA coupled with the absence of Disease Modifying Osteoarthritis Drugs (DMOADs) heightens the negative impact of this disease on humanity. Recent studies have shown that cytokines are important in the development and progression of OA. It has been hypothesized that neutralizing IL-12 or TNF-1 may provide benefit to OA patients, hence, biologics or drugs that neutralize these cytokines are being investigated. Clinical trials with an anti-TNF-1 antibody are currently ongoing. The alternative pathway (AP) of complement has recently been implicated in the etiology of OA. We have developed a proprietary group of antibodies that selectively target the AP without affecting the host defense mediated via the classical pathway (CP). Our preliminary results suggest that the AP plays an important role in the development and progression of OA and that our target antibody is highly effective in resolving OA as indicated by rabbit models of OA. The current application proposes development of a humanized IgG1 as a potent treatment for halting and arresting the progression of OA in humans. In the Phase I segment, we further test a specific neutralizing anti-complement monoclonal antibody in the young rabbit OA model. In the Phase II segment, we will study the efficacy of the targeted humanized antibody to aged rabbits, evaluate the efficacy of the biologic in multiple modes of administration, and establish protocol for scaled up preparation of the humanized antibody. Our studies will provide new insight into the development of novel therapies for the treatment of OA. Overall, the proposed work is a critical step in the direction of developing a cost-effective, efficacious and safe therapeutic agent for preventing joint damage caused by OA.